An Electric Trap: Electron‐Rich Carbonyl Axis Ends Slow Threading/Dethreading Exchange Dynamics of Pillar[5]arene Ring along Axis

Viologen axes with negative carbonyl ends such as carboxylic acid and carbonylethyl groups were synthesized. The threading/dethreading exchange dynamics of the pillar[5]arene ring and these axes were studied by variable‐temperature 1H NMR and two‐dimensional exchange spectroscopy NMR spectroscopies. The exchange rate increased on introduction of electron‐rich carbonyl ends into the axis: the exchange rate constants of the pillar[5]arene ring along the carboxylic acid‐ended and carbonylethyl‐ended viologen axes were ca. 2000 and 360 times smaller, respectively, than that along the alkyl‐ended viologen axis.